1. Technical Field
The present invention relates to a leak detection system which is capable of detecting in succession the presence or absence of a leak from a test piece such as a hermetically sealed vessel, pipe, valve, and the like.
2. Related Art
It has been known to use a leak detector in a leak test or leak detection in which the presence or absence of a trace amount of leak from a test piece such as a hermetically sealed vessel, pipe, valve, and the like is detected or inspected (see, e.g., patent document 1). The leak detector is provided with a mass spectrometer which is arranged: to ionize the gas molecules in the vacuum; and to select only the helium ions to cause them to be incident on an ion collector, thereby quantitatively detecting as the ion current the helium gas that has been leaked into the vacuum. The mass spectrometer is mounted, through a gate valve, on a branch pipe that is branched from an evacuation pipe leading from the vacuum chamber in which a vacuum atmosphere can be formed, to a vacuum pump.
A description will now be made of an example in which the above-described conventional leak detector is used to perform a leak test by disposing a hermetically sealed vessel such as a tank and the like inside a test chamber (vacuum chamber) in which a vacuum atmosphere can be formed. First, the hermetically sealed vessel as a test piece is housed into the test chamber. Then, the test piece is filled with helium gas and, at the same time, the test chamber is evacuated to make it into a vacuum atmosphere. Then, in case there is a leak from the test piece, the presence or absence of the helium gas that is mixed in the vacuum atmosphere is detected by the leak detector.
Generally, the filling of helium gas into the test piece is performed in the following manner. That is, first, the test piece is pressurized by introducing gas such as nitrogen, air, and the like into the test piece, thereby performing a so-called gross leak test. Subsequently, the gas is evacuated out of the test piece, followed by filling the test piece with helium gas. This kind of operation of filling the test piece with helium gas is ordinarily performed along with the operation of evacuating the vacuum chamber.
By the way, there are various kinds of test pieces which are different in volume. In addition, some of such test pieces have small-diameter connection ports for evacuating and supplying gas therethrough. Therefore, there are cases in which much time is required in supplying gas into, and evacuating gas from, the test piece. In such cases, rate-limitation is imposed by the helium-filling operation among the operations of gross leak test through the helium-filling operation. As a result, there is a disadvantage in that the cycle time in leak detection becomes long.    Patent document 1: JP-A-1998-38746.
In view of the above, this invention has a problem to provide a leak detecting system in which the cycle time can be prevented from getting longer and in which the leak test can be efficiently performed when a plurality of test pieces are subjected to leak tests in succession.